The present invention relates to a color image processing method and electronic color conversion device for receiving color image data corresponding to an arbitrary color space, processing the image data, and outputting the image data to a color image forming device in an output color space.
In a conventional image forming device, such as a color printer, color image data received from a host computer, monitor, scanner, or other image-generating device, is in the form of an input color space. Typically, each color in the input image is represented by a three-dimensional coordinate system, such as Red (R), Green (G), and Blue (B). The additive RGB color space is suitable for forming and viewing an image on a computer monitor. Each pixel in the image is represented by 24-bit data, consisting of 3 eight-bit bytes, where each byte component corresponds to a primary color of the color space. For the RGB color space, each pixel in the computer monitor can be represented with a combination of numerical values of Red, Green and Blue (R, G, B). The numerical value is one of 256 values, ranging from 0 to 255, that represents a level of the respective color component in the pixel. For example, a purely red pixel comprising an image on a computer screen will have the coordinates (255, 0, 0). In addition, input image data may correspond to a grey-scale color space. In this color space, each pixel is represented by one of 256 levels of intensity, ranging from 0 to 255. Each level represents an increment of grey between black (0) and white (255).
Generally, color images are formed using a subtractive CMY color space. Cyan (C), Magenta (M), and Yellow (Y) are the complementary colors of Red (R), Green (G) and Blue (B), respectively, and are used as the colors of the ink or toner in forming a hard copy of the image. Each combination of (R, G, B) in the input image corresponds to a combination of Cyan (C), Magenta (M) and Yellow (Y) in the output color image. In addition, Black (K) is often included with a CMY color space when forming images. In this case, the output color space is a CMYK color space. An alternate output color space for printing images is a grey-scale color space.
In order to form image data having the color spaces intended by a user, conversion from an input color space to an output color space must be performed. This involves converting data in the (R, G, B) color space to the (C, M, Y) or (C, M, Y, K) color space for most applications. An image-producing apparatus converts the input brightness RGB signals or signals having another color space, into density data in the (C, M, Y), (C, M, Y, K) or other output color space. Conventionally, this is done on a pixel by pixel basis using a conversion means. The conversion means usually includes a look-up table circuit, comprising a database indicating the coordinates of an output color space combination for a given input color space combination. The look-up table circuit performs a conversion calculation for each of the (R, G, B) image data.
The color conversion process is complicated and time-consuming. Every pixel must be individually processed and converted on a pixel by pixel basis. Even if neighboring pixels undergo the same conversion operation, the calculation must be repeated for every new pixel. This causes redundant calculations to be performed for pixels having the exact same combination of color values.